1. Field of the Invention
The present invention relates to a motorcycle that executes traction control.
2. Description of the Related Art
Conventionally, some motorcycles execute traction control for preventing an excessive slip of the rear wheel by reducing an engine torque. Such conventional motorcycles set target values (hereinafter referred to as a target slip value) for a slip value (that is, a slip amount that is a difference in the rotation speed between the front wheel and the rear wheel, or a slip ratio that is a ratio of the difference described above to the rotation speed of the rear wheel). In such a motorcycle, the engine is controlled such that an actual slip value calculated based on the difference in the rotation speed between the front wheel and the rear wheel follows the target slip value.
According to the motorcycle described in Japanese Patent Laid-open Publication No. 2008-111430, the target slip value is set in accordance with an accelerator opening degree such that a larger accelerator opening degree (the operation amount of the accelerator by the driver) leads to a higher target slip value. With the above configuration, it is possible not only to prevent an excessive slip of the rear wheel but also to realize a slip in accordance with an acceleration request of the driver. According to the motorcycle described in Japanese Patent Laid-open Publication No. 2008-111430, traction control starts after the actual slip value exceeds the target slip value, and thereafter, during execution of the traction control, an engine output torque (hereinafter referred to as an engine torque) is controlled based on the difference between the actual slip value and the target slip value such that the actual slip value follows the target slip value.
According to the motorcycle described in Japanese Patent Laid-open Publication No. 2008-111430, traction control starts after the actual slip value exceeds the target slip value. Thus, in order to make the actual slip value the same as the target slip value in a shorter period, a significant decrease in the engine torque is necessary at the start of the traction control, which deteriorates the comfort of riding.
In order to address the above problems, it may be an option that the traction control starts before the actual slip value reaches the target slip value. However, in Japanese Patent Laid-open Publication No. 2008-111430, the engine torque is controlled based on the difference between the actual slip value and the target slip value even when the actual slip value is lower than the target slip value. Therefore, start of the traction control according to Japanese Patent Laid-open Publication No. 2008-111430 before the actual slip value reaches the target slip value results in an increase in the engine torque which makes the actual slip value closer to the target slip value. That is, start of the traction control results in an increase in the engine torque irrespective of an accelerator operation by the driver. This consequently deteriorates the riding comfort.